Improve xml dump

[b-jonas0]

The current xml dumps are difficult to use. Change them in the following ways:

• Make dumps that show all highly voted definitions, not only the highest voted ones.
• Make dumps show all the hidden details that jbovlaste supposedly knows about but won't tell in the dump, such as who entered a definition, which words are a joke, etc.
• Make dumps more easy to accessible. The captcha you have to fill right now is quite tricky.
• If this would put too much traffic to jbovlaste, at least make incremental dumps that contain only the full data for entries modified in the last 6 months (make sure it also represents deletions) and make that available without a captcha. You may compress dumps if it helps, and make the xml not ampersand-escape apostrophes except inside apsotrophe-quoted attribute values.